This invention relates in general to the sensing of jams in electromechanical systems utilizing solenoids. More particularly, this invention relates to a solenoid engagement sensing circuit which senses a jam in a solenoid actuated shutter positioned between an electronic imaging device and a film processor.
Electromechanical systems utilizing solenoid actuated mechanisms are widely used in industry. In such systems it is desirable to determine if a mechanical and/or electrical failure has occurred in the solenoid actuated mechanism so that appropriate action can be taken to prevent damage to the system. Commercially available sensors are employed utilizing various techniques (such as optical or inductive proximity) for sensing mechanical position. These devices typically require additional wiring and bracketry which can adversely affect cost and reliability of the system. The following U.S. Patents disclose various solenoid actuated electromechanical systems which have solenoid sensing arrangements which are disadvantageous for one or more of the following reasons, i.e. undo complexity, excessive cost, unreliability, excessive space requirements, undesirable power consumption. U.S. Pat. No. 4,868,709, issued Sept. 19, 1989, inventor H. Aoki; U.S. Pat. No. 4,905,121, issued Feb. 27,1990, inventor T. Uetsuhara et al; U.S. Pat. No. 3,857,081, issued Dec. 24, 1974, inventor E. F. Gebelerein, Jr.; U.S. Pat. No. 4,205,307, issued May 27, 1980, inventors P. Liermann et al.; U.S. Pat. No. 3,678,344, issued July 18, 1972, inventor W. R. Wedmore; U.S. Pat. No. 4,456,943, issued June 26, 1984, inventor M. S. Judy; U.S. Pat. No. 4,661,766, issued Apr. 28, 1987, inventors J. P. Hoffman et al.; U.S. Pat. No. 4,967,309, issued Oct. 30, 1990, inventor J. P. Hoffman; U.S. Pat. No. 4,387,306, issued June 7, 1983, inventor H. C. Sibley; U.S. Pat. No. 4,538,203, issued Aug. 27, 1985, inventors P. D. Flanner et al.; U.S. Pat. No. 2,600,317, issued June 10, 1952, inventor G. W. Nagel.
Commonly assigned U.S. Pat. No. 4,851,959 discloses a useful technique for sensing jams in electromechanical systems involving solenoids. As disclosed in this patent, a disk memory library includes picker arms operated by a solenoid to remove a selected disk from a library stack of disks and to place the disk in a reading/writing environment. The solenoid plunger's position is determined by sensing its effect on a series resonant circuit including the solenoid coil and a series capacitor. A function generator provides a triangular signal to the solenoid coil. A threshold detector and synchronous detector determine when the plunger is in or out and, in turn, when the picker arms are extended or retracted. Although the solenoid engagement sensing circuit of the latter patent is useful for the purposes for which it is intended, it would be desirable to provide a solenoid engagement sensing circuit which has fewer components, which operates at higher frequencies and which is lower in cost.